This invention relates to a sunscreen formulation which contains a phenyl functional organosilicon compound. More particularly the invention is directed to a sunscreen additive which functions to enhance the absorbance of ultraviolet light by sunscreen chemicals.
The sun emits energy in a continuous band throughout the electromagnetic spectrum. The shorter wavelengths are absorbed in the upper atmosphere. At sea level, the radiation is present in a range of about 290-400 nanometers. The production of sunburn termed "erythema" and the production of melanin pigment occurs at about 297 nanometers. About twenty minutes of exposure to midsummer sunlight is required to produce a minimum perceptible sunburn on normal Caucasian skin. Products which protect the skin from excessive exposure have become increasingly widespread in view of the advent of scientific data linking prolonged exposure to sunlight to aging effects on skin and the implications of skin cancer. Sunscreen products include physical screening agents such as titanium dioxide and zinc oxide which are opaque materials that block and scatter light, thus acting as mechanical barriers. Chemical sunscreening agents, however, are capable of absorbing ultraviolet light and offer selective protection against certain ultraviolet wave bands depending upon the absorption spectrum of the particular chemical sunscreening agent. Accordingly, a sunburn preventive agent is an active ingredient which absorbs ninety-five percent or more of light in the ultraviolet range of 290-320 nanometers. A suntanning agent is an active ingredient which absorbs up to about eighty-five percent of light in the ultraviolet range of 290-320 nanometers, but which transmits light at wavelengths in excess of about 320 nanometers. An opaque sunblocking agent is an active ingredient which reflects or scatters light in the ultraviolet and visible range at wavelengths of 290-770 nanometers.
Although most people are aware of the harmful effects of overexposure to the sun, modern lifestyles include significant amounts of outdoor activities such as golf, hiking, skiing, bicycling, jogging, and sun bathing. These activities do increase exposure to the sun but often result in a desirable tan and overall healthy appearance. Suntan lotions and oils therefore afford some degree of protection against premature wrinkles and painful burns while allowing the users to reap the benefits of sunshine while simultaneously preventing significant damage.
It has long been recognized that one deficiency of suntan products has been the failure of the product to protect against overexposure because the sunscreening agent in the product becomes diluted or is floated from the skin surface by contact with water or by the generation of perspiration. It has been found that resistance to water and perspiration can be imparted to a sunscreen formulation by incorporating therein water repellents or emollients. A significant number of compounds have therefore been devised for this purpose, among which are organosilicon compounds. Thus, it is well known to employ siloxanes in suntan lotions, sprays, creams, and stick products, for the purpose of providing a non-oily emolliency to the sunscreen formulation. These siloxane compounds also function as a non-sticky water barrier, improve spreadability, and provide the sunscreen formulation with a smooth and silky feel when it is applied. Such siloxane compounds are also known to be skin lubricants functioning to add lubricity and softness to the skin. For example, a suntan oil is disclosed in U.S. Pat. No. 4,857,304, issued Aug. 15, 1989. The suntan oil contains a fluorocarbon, a sunscreen active agent of isooctyl p-dimethylaminobenzoate, perfume, and a phenyl functional polysiloxane having a viscosity of fifteen centistokes measured at twenty-five degrees Centigrade. While the compositions of the present invention also include a phenyl functional siloxane, the primary function of the siloxanes of the present invention is to enhance the absorbance of the sunscreen active ingredient for ultraviolet light, rather than to provide water repellency, emolliency, spreadability, lubricity, and skin softening and lubricating characteristics to the formulation, as in the '304 patent. Thus, according to the present invention, certain phenyl functional siloxanes have been found which actually increase the ultraviolet light absorbing power of sunscreen active ingredients. Prior to the present invention, this function of enhancing sunscreen absorbance has been alleged for materials such as proteins, amino acid complexes, and aromatic compounds containing multiple rings. It is heretofore not known to employ phenyl functional siloxanes for such a sunscreen ultraviolet light absorbance enhancing function.